The purpose of this project is the study of Aleutian disease (AD) of mink, a persistent infection by the Aleutian disease parvovirus (ADV). We have extended studies to include in situ hybridization using as hybridization probe radiolabeled molecularly cloned ADV DNA. Replication in cell culture was accompanied by the development of nuclear viral antigen and large numbers of autoradiographic grains over the nuclei of infected cells. This result contrasted markedly with findings made in tissues of infected mink. In spleen and mesenteric lymph node (MLN), ADV DNA was readily detected primarily in the cytoplasm or on the membranes of cells. Furthermore, in MLN grains were found localized to the periphery of germinal centers in a reticular pattern reminiscent of that described for protein antigens following immunization. Since viral antigens had the same distribution in these sections, this suggested that the DNA observed probably represented virus particles sequestered by elements of the immune system rather than sites of virus replication. Rare single cells contained grains localized over the nucleus, and this observation implied that the number of cells actually replicating ADV in these tissues was small. Extensive attempts were made to characterize infected cells by culturing infected in viro or in vivo with ADV. ADV replication could not be convincingly demonstrated although the lymphocytes were stimulated with mitogens and mink T cell growth factor. These results suggested that the target cell for ADV is either not a lymphocyte or that the conditions for its cultivation in vitro are exremely fastidious. In other studies, the possible role of interferons in the pathogenesis of ADV infections has been begun. ADV infection in cell culture induces interferon at both 31.8 degrees C and 37 degrees C, although the induction at 37 degrees C is much more rapid than that at 31.8 degrees C. Because ADV replicates only at the lower temperature, this finding may suggest a potential role for interferon in the suppression of ADV replication at 37\degrees C.